NB-IOT AND LTE CAT-M1 FIELD MEASUREMENTS AND SLA VERIFICATION - KEYSIGHT
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A P P L IC AT ION NO T E NB-IoT and LTE Cat-M1 Field Measurements and SLA Verification
Introduction
Internet of Things (IoT) is today’s megatrend in wireless communication industry. Machine-to-machine
(M2M) wireless connectivity is being adopted in various verticals at increasing pace. The number of IoT
devices deployed by 2020 is expected to increase to approximately 20 billion.
Cellular IoT (CIoT) is defined as a set of technologies under the 3GPP umbrella to enable IoT connectivity
using the licensed frequencies, co-existing with the legacy cellular broadband technologies, such as LTE,
UMTS and GSM. The main CIoT technologies being rolled out globally are NB-IoT and LTE Cat-M1. The term
CIoT is used to make the distinction to non-3GPP IoT technologies, such as LoRa and SigFox, which are
deployed in unlicensed bands.
IoT applications can be categorized to massive IoT and critical IoT. Massive IoT includes smart metering,
home security, etc. The requirements for massive IoT include years of battery life, scalability to very large
number of devices, robust coverage, and deep indoor facilities. The NB-IoT technology is optimized for this
use case. Critical IoT includes applications, such as health care and connected car, where very low latency
levels on ultra-reliable networks, often combined with very high throughput is required. LTE Cat-M1 is
optimized to meet these requirements.
LTE Cat-M1 NB-IoT
Heritage LTE Clean-slate
Bandwidth (downlink) 1.4 MHz 180 kHz (12 by 15 kHz)
Bandwidth (uplink) 1.4 MHz Single-tone (180 kHz by 3.75 kHz or 15 kHz) or
multi-tone (180 kHz by 15 kHz)
Multiple access (downlink) OFDMA OFDMA
Multiple access (uplink) SC-FDMA Single-tone FDMA or multi-tone SC-FDMA
Downlink peak bitrate 1 Mbps 250 kbps
Uplink peak bitrate 1 Mbps 250 kbps (Multi-tone)
20 kbps (Single-tone)
Latency 10 ms to 15 ms 100 ms ~8 s
Coverage (link budget) ~156 dB ~164 dB in standalone deployment
~149 dB in/guard-band deployment
Mobility Full Nomadic
Applications Critical IoT: Health care, home care, Massive IoT: Smart metering, home security, etc.
traffic SoC, connected car, etc.
Table 1. Comparison between LTE Cat-M1 and NB-IoT.
Find us at www.keysight.com Page 2Cellular IoT Field Testing – Verifying the Real Performance The emergence of IoT poses various challenges for network operators as well as for industrial customer verticals and M2M connectivity providers. What level of Quality of Service (QoS) and Service Level Agreements (SLAs) can be achieved and committed to? Are there any differences in performance between network equipment manufacturers, IoT device manufacturers, and different operators? How should the network be configured and planned to achieve optimal performance? Is the service coverage network wide, including deep inbuilding? How long is the battery life of my IoT device? Answers to these questions depend on the field performance of the commercial network equipment and IoT devices, interoperability between the equipment, and the network design and configuration. The 3GPP specification provides boundaries for the performance and operation of IoT, but the equipment implementations and the network design play major roles on the real field performance. Hence, field measurements are needed to obtain definite answers. Specifications vs. commercial implementations The 3GPP standard defines the technologies to deliver the key features of IoT, but many of the details on how these technologies are used and implemented are proprietary and vendor-specific. Further, the device antennas and housing may have significant impact on the practical performance achieved. Hence, the testing and benchmarking of network equipment manufacturers as well as the devices available in the market is crucial to verify the interoperability and performance of the equipment to be deployed. In this initial field/lab testing phase, tools providing a holistic view from the application-level down to RF metrics and control plane signaling are needed. Figure 1. Signaling flow of NB-IoT device connection as seen from Keysight’s Nemo Outdoor data collection tool. Find us at www.keysight.com Page 3
Signal coverage IoT is designed to offer better coverage when compared to existing mobile broadband technologies. The maximum coverage gain over regular LTE is expected to be 23 dB for NB-IoT and 15 dB for LTE Cat-M1. The real gain may be less, depending on the deployment method and configuration. Increased coverage enables operators to deploy cellular IoT technologies in the existing LTE base station grid, achieving deep inbuilding coverage with or without reduced additional indoor cell and DAS deployments. The target is to provide sufficient coverage for smart meters and other IoT appliances that are typically located in basements and similar deep inbuilding locations. Since IoT coverage is better than with any of the existing cellular technologies, and the existing base station grid is designed to provide sufficient coverage for established cellular broadband technologies such as LTE, no major coverage issues are expected in outdoor environments when IoT is deployed in the existing base stations. When the IoT coverage is verified with measurements, the focus must be on deep inbuilding to push the system to the designed performance limits, and to gather an understanding on how deep the indoor coverage really is. Service coverage Another important point to consider when testing NB-IoT is service coverage. Determining the IoT coverage is not simply a matter of signal strength and block/bit error rate. Coverage in both NB-IoT and LTE Cat-M1 is improved most at the expense of latency, bandwidth, and spectral efficiency. One of the key techniques used is repetition, that is, redundant transmissions of the same frame multiple times, and combining the repeated transfers at the receiving end. Every repetition increases the coverage by 3 dB, assuming ideal channel estimation and TX/RX chain. However, the latency experienced by the application is doubled, and throughput and spectral efficiency are sliced to half. As a result, round trip time may be increased up to ~10 s and throughput decreased down to 100 bps in extreme low coverage. As discussed, spectral efficiency is also decreased drastically in extreme low coverage. This goes easily unnoticed at the early stages when the IoT network capacity is not yet limited, but will have a big impact down the road when the IoT technologies are widely adopted and the number of users in a cell increase to thousands. A seemingly small difference in the number of repetitions needed has a huge impact on the number of IoT users that can be accommodated in a cell. It is important to first establish the minimum accepted QoS in terms of latency and bit rate, and then verify the coverage against that boundary. This must be kept in mind also when benchmarking the performance of network equipment and/or IoT devices. All equipment may reach the extreme coverage, but with very different QoS levels. The only way to verify service coverage accurately is to perform active tests with an IoT device connected to a measurement tool SW and to generate load over the connection between the device and the network with a test protocol, such as Ping. The measurement application collects the application performance readings, as well as the radio metrics, by tapping into the diagnostics interface of the IoT modem/chip of the device. The outcome of the service coverage test is the minimum signal coverage and quality threshold for achieving acceptable QoS. Once the thresholds are known, network scanners can be used to measure the signal coverage and quality in a wider area more efficiently. Scanners can simultaneously measure the signal strength of all cells, from all operators, making it possible to assess the coverage accurately enough for optimization, troubleshooting, and benchmarking purposes. The scanner results can then be mapped with service coverage results. Find us at www.keysight.com Page 4
Figure 2. Cat-M1 service coverage (RTT - round trip time) verification results from live network active tests using Keysight’s Nemo Analyze post- processing tool. IoT devices typically measure only serving cell quality and coverage during an active connection, not neighbor cells. In NB-IoT this is because the standard does not support seamless mobility and handover. In LTE Cat-M1 handovers are supported according to the 3GPP specification but not configured in all live networks due to power saving reasons. Hence, IoT devices cannot be used to collect signal coverage and quality readings comprehensively in drive testing, and scanners will be needed for this purpose. On the other hand, it is more important to start performing active tests using IoT devices to verify the service coverage. Also, IoT testing is expected to focus on inbuilding where stationary and low mobility testing is performed, and scanner measurements are less important. Find us at www.keysight.com Page 5
Battery life and power consumption The power consumption of IoT devices is another important factor, directly linked to the coverage as well as to network design and configuration. Both LTE Cat-M1 and NB-IoT are designed to significantly decrease power consumption over broadband cellular technologies. The key power saving technique is DRX (discontinuous reception) in a few different flavors. The main principle in these techniques is that the modem is effectively switched off during idle periods. In NB-IoT, the maximum battery life expected is in the range of 10 years in applications where small data packets are sent sporadically. Long battery life is important for many low- cost, unmanned IoT sensor applications. Ideally the battery should last for the whole lifecycle of the device to avoid costly maintenance. Coverage has a big impact on the battery life. In low coverage, more repetitions are needed to successfully transfer the data. The more repetitions, the longer the duty cycles of the IoT modems and higher the power consumption, respectively. Excess repetitions due to network misconfiguration or network implementation also have a similar impact. In a given deep inbuilding location, there may be a difference of tens of dBs in the coverage between operators. This can result in years of difference in the maximum battery life of an IoT device deployed in that location. Hence, coverage remains an important benchmark KPI between operators. Summary Cellular IoT performance is heavily dependent on IoT devices, network equipment implementation, interoperability between the equipment, and network design. Field measurements are important for operators and industrial IoT customers to verify and benchmark the performance of IoT solutions. Enhanced coverage is one of the key features of Cellular IoT. The coverage boost is achieved at the expense of quality of service (QoS). Hence, active testing and verification of both QoS and signal coverage are needed to understand and benchmark the true service coverage. Coverage also has a direct impact on the network capacity and device power consumption. Keysight Network Testing develops and sells RF measurement and analysis equipment under the Nemo brand. Nemo Outdoor drive test solution has been used by operators in multiple pilots and coverage measurements in IoT networks. www.keysight.com/find/nemo Learn more at: www.keysight.com For more information on Keysight Technologies’ products, applications or services, please contact your local Keysight office. The complete list is available at: www.keysight.com/find/contactus Find us at www.keysight.com Page 6 This information is subject to change without notice. © Keysight Technologies, 2015 - 2019, Published in USA , May 16, 2019, 5992-2747EN
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